Multi-anode device and methods for sputter deposition

ABSTRACT

A method and apparatus for vacuum coating plural articles employs a drum work holder configuration and a sputter source with a plurality of individually controlled anodes for effectively providing uniform coatings on articles disposed at different locations on the drum work holder. A small number of measured process parameters are used to control a small number of process variable to improve coating uniformity from batch to batch.

[0001] This application is a divisional of copending U.S. patentapplication Ser. No. 09/605,401, “Multi-Anode Device and Methods forSputter Deposition”, filed on Jun. 28, 2000.

FIELD OF THE INVENTION

[0002] The present invention relates to methods and apparatus forsputter coating articles, and especially, for reactive sputter coatingof plastic ophthalmic lens elements using a sputter source with multipleanodes. As used herein, lens elements include, according to context,edged lenses, semi-finished lenses and lens blanks. Also included arewafers for forming laminate lenses or wafer blanks therefor. Ophthalmicuses of the lens elements include uses in eyeglasses, goggles andsunglasses.

BACKGROUND AND OBJECTS OF THE INVENTION

[0003] Many ophthalmic lenses produced today are made from a singleplastic body or laminated plastic wafers. The plastic material mayinclude thermoplastic material such as polycarbonate or thermosetmaterial such as diallyl glycol carbonate types, e.g. CR-39 (PPGIndustries). The material may also be a cross linkable polymeric castingcomposition such as described in U.S. Pat. No. 5,502,139 to Toh et al.and assigned to applicant.

[0004] Ophthalmic lens elements are frequently coated to achieve specialproperties. Anti-reflection coatings improve the transmittance ofvisible light and the cosmetic appearance of the lenses. Reflective andabsorptive coatings may be employed in sun lenses to reduce lighttransmittance to the eye, to protect the eye from UV radiation and/or toimpart cosmetic colorations to the lens. Coatings may also provide otherbeneficial properties such as increased hardness and scratch resistanceand anti-static properties.

[0005] Desirable lens coatings may be created by applying single ormultiple layers of metal, metal oxides or semi-metal oxides to surfacesof the lens element. Such materials include oxides of silicon,zirconium, titanium, niobium and tantalum. Metal and semi-metal nitridesare also used. Examples of such multilayer coatings are given, forexample, in U.S. Pat. No. 5,719,705 to Machol entitled “Anti-staticAnti-reflection Coatings”, assigned to applicant. Interference filtercoatings for sunglasses are disclosed, for example, in U.S. Pat. No.2,758,510 to Auwarter. Other lens coatings are disclosed inInternational Application WO 99/21048 to Yip, et al., which is herebyincorporated by reference.

[0006] Various methods are disclosed in the prior art for applying metaland semi-metal oxide coatings to ophthalmic lenses. Such coatings havetraditionally been deposited by means of thermal evaporation, and morerecently, by electron-beam (e-beam) evaporation and reactive sputtering.Evaporations are typically carried out at vacuums better than 10E-5Torr. Ritter et al. U.S. Pat. No. 4,172,156, for example, disclosese-beam evaporation in an oxygen atmosphere of Cr and Si to form coatinglayers on a plastic lens. The use of reactive sputter deposition to formvarious oxide layers on lens elements is disclosed in theabove-mentioned '705 patent to Machol.

[0007] Reactive sputtering in general is a conventional technique oftenused, for example, in providing thin oxide coatings for such items assemiconductor wafers or glass lamp reflectors. Examples of variousconventional vacuum deposition systems for the formation of coatings byreactive sputtering are disclosed in the following patents: U.S. Pat.No. 5,616,224 to Boling; U.S. Pat. No. 4,851,095 to Scobey et al.; U.S.Pat. No. 4,591,418 to Snyder; U.S. Pat. No. 4,420,385 to Hartsough;British Patent Application GB 2,180,262 to Wort et al.; Japanese KokaiNo. 62-284076 to Ito; and German Patent No. 123,714 to Heisig et al.

[0008] The coating of plastic lenses in spinning drum coaters by meansof sputtering technology, including DC reactive sputtering, is arelatively recent development. A conventional drum vacuum coating systemused for this purpose is shown in FIG. 1. The system includes a vacuumchamber 11, which contains a hollow workpiece holder or drum 12. Lenselements, such as lens 13 are arranged in columns on an external surfaceof the drum 12. A coating applicator 14 is located near a wall of thevacuum chamber adjacent the drum 12. The coating applicator 14 maycomprise a combination of magnetron sputtering sources and microwaveplasma generators with a reactive gas supply such as disclosed in U.S.Pat. No. 5,616,224 to Boling, which is hereby incorporated by reference.Power is delivered to the coating applicator 14 by one or more powersupplies (not shown) via an electrical lead assembly 17. A reversingpower supply for arc suppression such as disclosed in U.S. Pat. No.5,616,224 to Boling may be included. A sputtering gas is introduced intothe vacuum chamber through gas-supply plumbing built into the coatingapplicator or through a separate port (not shown) on the vacuum chamber11. The sputtering gas is controlled by a gas controller (not shown) andmay be an inert gas such as argon or a reactive gas mixture such asargon/oxygen or argon/nitrogen.

[0009] The vacuum chamber 11 is evacuated by vacuum pumps (not shown)attached to a pumping plenum 15. A cryopumping surface, known as aMeissner trap, is conventionally provided in the form of cryocoils 16 inthe plenum 15. A coolant with a temperature well below the freezingpoint of water flows through the cryocoils 16, allowing the Meissnertrap to remove water vapor from the vacuum chamber 11. A Meissner trapmay be advantageously configured in the vacuum chamber 11 rather than inthe pumping plenum 15 to improve the cryopumping of water vapor. Such aconfiguration is especially useful when coating plastic lens elementsbecause plastic lens elements have a tendency to outgas substantiallymore water vapor than conventional glass lenses, as disclosed in U.S.Pat. No. 6,258,218, hereby incorporated by reference.

[0010] A drum vacuum coating system with an elongated magnetron sputtersource 14 such as that illustrated in FIG. 1 provides a convenient meansof coating numerous lens elements or other articles. However, Applicantshave observed that such systems typically do not produce uniformly thickcoatings on multiple articles disposed in a given column of the drum 12due to the variation in sputter rate along the length of the sputtersource. In other words, an article or lens element positioned near thetop of a given column may not receive a coating of the same thickness asan article or lens element positioned near the center of that column.

[0011] Several methods directed toward improving coating uniformity ofsputtered films have been disclosed in the prior art. U.S. Pat. No.5,645,699 issued to Sieck discloses a system comprising two cylindricalmagnetron sputter sources, each with an anode substantially spanning thelength of the sputter source, wherein the placement of a third anodebetween the two sputter sources has improved coating uniformity. U.S.Pat. No. 4,849,087 issued to Meyer discloses the use of multiple gasnozzles distributed along the length of a sputter source to delivervarying amounts of an argon/oxygen gas mixture to local regions of theplasma above the sputter target (cathode). Individual resistance probesdisposed along the width of the substrate measure the local resistanceof the coating and provide feedback signals to adjust the gas flowthrough the various nozzles to maintain uniform electrical resistance invarious regions of the coating. While this approach provides control ofthe electrical resistance of the coating, it does not necessarilyprovide control of the coating thickness, a quantity of importance foroptical coatings.

[0012] U.S. Pat. Nos. 5,487,821 and 5,683,558 to Sieck et al. disclosethe use of “wire brush” anodes in conjunction with magnetron sputtersources and indicate that the wire-brush point density of an anode maybe adjusted along the length of the sputter source to affect theuniformity of the deposited film. U.S. Pat. No. 5,616,225 issued toSieck et al. discloses the use of wire brush anodes and the use ofmultiple anodes in conjunction with a single magnetron sputter cathodefor coating substrates (especially large substrates) wherein the anodevoltages may be individually controlled. The '225 patent indicates thatthis control may be utilized to improve the thickness uniformity of thedeposited coating. The disclosure in the '225 patent, however, does notaddress controlling the thickness uniformity of reactive coatingsdeposited on large numbers of individual lens elements using anelongated magnetron sputter source in a drum vacuum coating system.

[0013] A need still exists to provide drum vacuum deposition systems forhigh volume production of individual articles, such as plastic lenselements, while ensuring a high degree of control over the thickness andcomposition of the coatings.

[0014] Accordingly, it is an object of the present invention to improvethe degree of control over the thickness and composition of thin metaland semi-metal oxide coatings deposited on multiple articles,particularly plastic lenses, disposed on a rotatable holder in a vacuumcoating system.

[0015] It is another object of the present invention to provide amulti-anode sputter source adapted to the geometry of a cylindrical drumvacuum coating system for depositing coatings on numerous plastic parts.

[0016] It is another object of the present invention to provide anapparatus for depositing a high quality coating on large numbers ofplastic lens elements in a system which is relatively inexpensive toconstruct and operate.

[0017] These and other objects and features of the present inventionwill be apparent from the written description and drawings presentedherein.

SUMMARY OF THE INVENTION

[0018] A drum vacuum coating system with an elongated magnetron sputtersource provides a convenient means of coating numerous lens elements orother articles located on a rotatable drum. However, Applicants haveobserved that such systems typically suffer from the inability toproduce coatings of uniform thickness on multiple articles disposed invarious locations on the drum due to variations in the sputter ratealong the length of the sputter source. Applicants have determined thatproviding an elongated sputter source with multiple anodes, wherein thecurrents to the anodes may be individually controlled or controlled inpairs, allows the deposition of coatings of substantially uniformthickness on multiple articles regardless of their position on the drum.The thickness uniformity is acceptable for thin optical coatings onophthalmic lens elements.

[0019] A preferred embodiment of the present invention is a method andapparatus for sputter coating a plurality of articles such as plasticlens elements. The system includes a vacuum chamber, a rotatablecylindrical holder for holding the plurality of articles, and at leastone sputter source that is elongated along a lengthwise direction andthat has a cathode and a plurality of anodes. The sputter source isdisposed with its lengthwise direction parallel to a rotation axis ofthe cylindrical holder, and the anodes are disposed adjacent the cathodesubstantially along at least one line parallel to the lengthwisedirection. The articles may be disposed in a predetermined pattern onthe cylindrical holder, and the anodes may be disposed in positionscorresponding to positions of the articles disposed on the cylindricaldrum. Additionally, the articles may be arranged in columns and rows onthe cylindrical holder, the columns being parallel to the rotation axisof the cylindrical holder, and the anodes may be configured in pairs,each anode pair being aligned with a row on the cylindrical holder. Thesputter source may be a planar magnetron sputter source.

[0020] A cathode power supply provides a negative voltage to thecathode, and a separate anode power supply with a plurality of channelsprovides anode currents to the anodes. Alternatively, the cathode powersupply and the anode power supply may be provided in a single unit. Theanodes may be configured in pairs, and each anode pair may be powered bya separate channel. In addition, the anode currents may be adjusted in amanner to produce coatings of increased uniformity of thickness onarticles positioned in different locations on the cylindrical holder. Inone embodiment, the same amount of current is provided to each activeanode pair by the controlled power supply.

[0021] The length of the sputter source may range from twenty inches tosixty inches, though approximately forty inches is a preferred length.The number of pairs of anodes may range from six pairs to fifteen pairs.Eight or nine pairs of anodes are preferred. In addition, it ispreferred that the length of each anode is approximately the same as thediameter (height) of the surface of article to be coated. The height anddiameter of the drum may be approximately forty inches, and the drum mayhold approximately 200 to 400 articles.

[0022] In order to prevent the buildup of dielectric material on theelectrically active anodes each anode of the sputter source may beconfigured as an electrically conducting bar having a recessed slot, theslot being oriented such that the opening of the slot is directed awayfrom the cathode. In this manner, anodes are provided with interiorsurfaces that remain substantially free of dielectric coatings, ensuringgood electrical conduction between the anodes and the sputter plasma.Alternatively, the anodes may be configured as wire-brush anodes,wherein each anode comprises a plurality of electrically conductingwires emanating from an electrically conducting support member. Thisconfiguration similarly provides anode surfaces that remainsubstantially free of dielectric coating deposits at the root of thebrush.

[0023] In another embodiment, the apparatus may be used to carry outreactive DC sputtering of a thin coating, which may comprise adielectric layer deposited onto surfaces of plural articles such asplastic lens elements. In this case, the apparatus again includes avacuum chamber and a sputtering source that is elongated in a lengthwisedirection and that has a cathode and a plurality of anodes, the anodesbeing arranged in pairs. The apparatus also includes a rotatable articleholder located in the vacuum chamber that rotates the plural articlespast the sputtering source, the articles being arranged in apredetermined pattern on the article holder. The article holder may be ahollow drum rotated about its central axis. In addition, the apparatusincludes a source of reactive gas, such as oxygen or nitrogen. Anelongated plasma applicator, such as a microwave plasma generator, isalso provided adjacent to the sputtering source for producing a plasmato facilitate the reaction of the reactive gas with material sputteredfrom the sputtering source. The sputter source may be a planar magnetronsputter source.

[0024] The articles may be arranged in columns and rows on the articleholder, each anode pair being aligned with a row on the cylindricalholder. The reactive sputtering may comprise the sputtering of a metalor semi-metal utilizing a sputtering gas that contains oxygen in orderto produce metal-oxide or semi-metal-oxide coatings. A sputtering gascomprising nitrogen may also be used to produce nitride coatings. Inaddition, a second sputtering source may be provided adjacent to thefirst sputtering source or adjacent to a plasma applicator forsputtering a metal or semi-metal different than that sputtered from thefirst sputtering source. In this manner, multiple coatings withdifferent indexes of refraction may be provided on articles such asplastic lens elements.

[0025] The apparatus may further comprise a controller that receives aninput signal corresponding to a small number of measurable processvariables (for example, two) and which controls a small number ofprocess variables (for example, two) in response thereto. In a preferredembodiment, the measurable process variables are cathode voltage andtotal gas pressure; the controlled variables are a first flow rate for afirst gas and a second flow rate for a second gas. A purpose of thecontroller is to maintain batch-to-batch uniformity of coating thicknessand coating composition. The controller may be used in roll coating orthe coating of discrete articles such as lens elements as describedbelow.

[0026] Batch to batch (run to run) stability of deposition rates of thesputtered materials may vary due to a number of causes even when thesputter plasma is held at a constant power dissipation. These causesincludes: historical effects on the target (such as oxide coverage andoxygen implantation), target cleaning, tooling cleaning, chambercleaning, length of time the chamber is opened for loading, unloading orservicing and consequent coverage of chamber and tooling with absorbedlayers of water vapor, thickness of deposited materials on tooling andchamber, type of plastic constituting the lens substrates and theirdegree of water uptake, gas leaks, improper calibration of partialpressure gauges and/or other means of measuring partial pressures suchas Optical Gas Controllers. Applicants have determined that, at constantsputter plasma power or constant sputter cathode current, more stabledeposition rates may be obtained by manually adjusting two directlycontrollable process variables (in a preferred embodiment, the flowrates of the buffer gas (usually Argon) and the reactive gas (usuallyoxygen)) according to a set of rules based on observations of twomeasured input parameters (in a preferred embodiment, cathode voltageand total pressure). The rules may be experiential rules based on anexpert's understanding of the operation of a particular sputteringsystem. These rules may be embedded in the fuzzy logic control system.For example input parameters may include classifying three levels ofcathode voltage and total pressure: “LOW”, “OK” and “HIGH”. The outputparameters for adjusting the operation of the system may include threeclassifications for the flow rates of the buffer gas and the flow rateof the reactive gas, namely: “INCREASE”, “HOLD” and “DECREASE”. Thefuzzy logic determination may be implemented in control signals foropening or closing buffer gas and reactive gas valves by a preciseamount.

[0027] In another embodiment, a multi-anode device for use in sputterdeposition is provided. Note that the multi-anode device may be usedseparately from the above described gas control techniques. However,both techniques may be advantageously used to achieve a high degree ofcoating thickness uniformity.

[0028] The multi-anode device comprises a cathode and a plurality ofanodes located in predetermined positions adjacent to first and secondopposing sides of the cathode. The anodes disposed at each of the firstand second opposing sides of the cathode are configured in a regulararrangement to substantially minimize or eliminate gaps between adjacentanodes. Further, a different current may be applied to each anode. Sucha configuration may be desirable for facilitating uniformity of thesputter plasma. In particular, the anodes at a given side of the cathodemay be configured in a sawtooth arrangement, wherein an end of one anodeis disposed closer to the cathode than an end of the adjacent anode. Theanodes at opposing sides of the cathode may be arranged identically orin a mirror image arrangement. The anodes may also be arranged in anessentially linear fashion wherein the ends of the anodes approach eachother closely but are shielded from one another by interposing anelectrical and/or physical barrier between said ends. In anotherembodiment, the ends of adjacent anodes may be purposely separated from,for example, 1 to 5 inches to modify electrical coupling of the anodeswith one another through the plasma.

[0029] In addition, each anode of the multi-anode device may beconfigured as an electrically conducting bar having a recessed slot, theslot being oriented such that the opening of the slot is directed awayfrom the cathode. Alternatively, the anodes may be configured aswire-brush anodes, wherein each anode comprises a plurality ofelectrically conducting wires emanating from an electrically conductingsupport member.

[0030] In another embodiment, a method for sputter coating a pluralityof articles is provided. A vacuum chamber is provided having at leastone sputter source with a plurality of anodes configured in pairs andhaving an article holder that rotates about an axis. Plural articles arelocated in a predetermined pattern on a radially outward facing surfaceof the article holder, and the chamber is pumped down. A sputtering gasof the desired composition, flow and pressure is provided, and thearticle holder is rotated relative to the sputter source. Sputtercoating is carried out on the radially outward facing surfaces of thearticles while controlling current to each pair of anodes separately.

[0031] The articles may be arranged in columns and rows on the outwardfacing surface of the article holder, and the rows may be aligned withpairs of anodes. The drum may be continuously or sequentially rotatedrelative to the sputter source or sputter sources while voltages areapplied to the cathode and anodes to cause material to be sputtered fromthe sputtering target onto the radially outward facing surfaces of thearticles. Further, the currents to the anodes may be adjusted in amanner to provide a uniform coating to the articles at all positions onthe article holder. In addition, the sputter coating may comprise areactive DC process in which sputtered material reacts with reactant gasto form a dielectric layer. The dielectric layer may comprise at leastone layer of a metal oxide or semi-metal oxide. The articles may beplastic lens elements, and the sputter source may be a planar magnetronsputter source. In one embodiment of the invention the individualcurrents to be applied to each anode pair for each target material, inorder to adjust uniformity, are determined before each coating batch byspectral measurements or otherwise on articles or witness samples coatedduring prior batches.

[0032] The foregoing has been provided as a convenient summary ofaspects of the invention. The invention intended to be protected is,however, defined by the claims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a pictorial view in partial phantom of a system known inthe prior art for vacuum coating plural plastic lens elements;

[0034]FIG. 2 is a pictorial view in partial phantom of drum vacuumcoating system according to one embodiment of the present invention;

[0035]FIG. 3 is a pictorial view of a multi-anode planar magnetronsputter source such as that shown in FIG. 2;

[0036]FIG. 4(a) is an illustration in side view of a multi-anode sputtersource according to the present invention with anode pairs configured inzones corresponding to article positions on the drum holder;

[0037]FIG. 4(b) is an illustration of an inside view of a portion of amulti-anode sputter source showing controlled current sources and anodeshielding of a preferred embodiment of the present invention;

[0038]FIG. 5(a) is an illustration in side view of an anodeconfiguration according to another embodiment of the present invention;

[0039]FIG. 5(b) is an illustration in side view of another anodeconfiguration different than that shown in FIG. 5(a);

[0040]FIG. 5(c) is an illustration in side view of an individual anodefor the embodiments illustrated in FIGS. 5(a) and 5(b);

[0041]FIG. 5(d) is a pictorial view of an individual anode having a slotfor maintaining an uncoated anode surface;

[0042]FIG. 6(a) is an illustration in side view of a wire-brushconfiguration of multiple anodes for a planar magnetron sputter sourceaccording to another embodiment of the present invention;

[0043]FIG. 6(b) is an illustration in plan view of an individual wirebrush anode for the embodiment illustrated in FIG. 6(a);

[0044]FIG. 6(c) is a cross-sectional view of a wire brush anode for theembodiment illustrated in FIG. 6(a);

[0045]FIG. 7(a) is a pictorial illustration of a multi-channelhigh-current power supply for use with a multi-anode sputter source;

[0046]FIG. 7(b) is a pictorial illustration of an optional computercontroller for use with the power supply illustrated FIG. 7(a);

[0047]FIG. 8 is a block diagram illustrating a fuzzy-logic controlmethod according to the present invention;

[0048]FIG. 9 is a flow diagram illustrating a fuzzy logic technique of apreferred embodiment of the present invention;

[0049] FIGS. 10(a) and 10(b) are plots of class membership as a functionof cathode voltage and pressure, respectively, for a system presented asan example embodying teachings of the present invention;

[0050]FIG. 11 presents details of the calculations performed in anillustrative Example of the implementation of techniques of the presentinvention;

[0051] FIGS. 12(a) and (b) are depictions of three dimensional controlsurfaces usable in an embodiment of the present invention.

DETAILED DESCRIPTION

[0052] The disclosed embodiments address the need for effective controlover the thickness of a deposited coating, particularly in systemscontaining drum workpiece holders and elongated magnetron sputtersources for coating numerous plastic lens elements.

[0053] A first embodiment according to the present invention is a drumvacuum coating system 20 incorporating an elongated, planar magnetronsputter source 30 with a target (cathode) 32 and multiple anodes 33-1through 33-N where N is the total number of anodes as illustrated inFIG. 2. The system 20 includes a vacuum chamber 21 with a pumping plenum25 attached to vacuum pumps (not shown) for the purpose of evacuatingthe chamber 21. The chamber 21 contains a hollow, rotating drum 22 shownin partial phantom. Articles 23, such as plastic lens elements may bearranged in columns and rows on an external surface of the drum 22. Themulti-anode sputter source 30 (described further below) is located neara wall of the vacuum chamber adjacent the drum 22. A hinged door (notshown) or a detachable top plate (not shown) may be used to provideaccess to the vacuum chamber 21 for loading articles 23 onto the drum22.

[0054] A sputtering gas is introduced into the vacuum chamber throughgas-supply plumbing built into the sputter source 30 or through aseparate port 24 to the vacuum chamber 21. The sputtering gas iscontrolled by a mass-flow controller (not shown) and may be an inert gassuch as argon or a reactive gas mixture such as argon/oxygen orargon/nitrogen for carrying out DC reactive sputtering.

[0055] A Meissner trap in the form of cryocoils 26 is optionallyprovided at the base of the chamber 21 and is especially beneficial whenthe articles to be coated are plastic lens elements, which may outgaswater vapor at a substantial rate. A similar Meissner trap (not shown)may optionally be provided at the top of the chamber. A coolant with atemperature well below the freezing point of water flows through thecryocoils 26, allowing the Meissner trap to remove water vapor from thevacuum chamber 21, improving the quality of the coatings as disclosed inU.S. Pat. No. 6,258,218.

[0056] Power is delivered to the multi-anode sputter source 30 by one ormore power supplies (not shown) with optional computer control via anelectrical lead assembly 27. As illustrated in FIG. 3, a negativecathode voltage −V_(C) is applied to the target, and anode currentsI_(A1) through I_(AN) are individually applied to the anodes. Bycontrolling the voltages to the anodes individually, the spatialdistribution of the plasma may be controlled to a large extent, thusallowing control of the rate of ejection of the target atoms fromdifferent regions of the target 32 defined by the positions of theanodes. Thus, individual control of the anode currents providesadditional control over the thickness of coatings deposited on articles23 positioned in proximity to the anodes. Arc suppression may beemployed.

[0057] As shown in FIG. 2, plasma applicators 28 and 29, such as thosedescribed in U.S. Pat. No. 5,616,224 to Boling, may optionally be placedat each side of the sputter source 30 to provide additional sources ofplasma that diffuse into the region above the target 32 of the sputtersource 30. The additional plasma provided by the plasma applicators 28and 29 may provide reduced arcing, enhanced deposition rate, andenhanced reaction of freshly deposited metal species in DC reactivesputtering. Power is delivered to the plasma applicators 28 and 29 byone or more power supplies (not shown) via electrical lead assemblies(not shown).

[0058] The coating process is carried out by first placing a collectionof articles 23 in columns and rows on a radially outward facing surfaceof the drum 22. The vacuum chamber 21 is then pumped down to a desiredbase pressure, and a sputtering gas of the desired composition, flow andpressure is provided. The drum 22 is then rotated relative to thesputter source 30, and voltages are applied to the target (cathode) 32and to the anodes to cause material to be sputtered from the sputteringtarget 32 onto the radially outward facing surfaces of the articles 23.The currents to the anodes are adjusted in a manner to provide a uniformcoating to the articles at all positions on the drum 22. As mentionedabove, the coating process may comprise a reactive DC process in whichsputtered material reacts with reactant gas to form a dielectriccoating. The drum 22 may be rotated continuously during the sputteringprocess, for example, at about 90 rpm.

[0059] Optionally, one plasma applicator rather than two plasmaapplicators as illustrated in FIG. 2 may be disposed adjacent to themulti-anode sputter source 30. Further, a configuration comprising twoor more multi-anode sputter sources rather than one multi-anode sputtersource 30 (as illustrated in FIG. 2) may be utilized. In a preferredembodiment, a plasma applicator may be disposed adjacent two multi-anodesputter sources, so that a substrate to be coated first encounters afirst sputter source, then a second sputter source and finally themicrowave applicator. Only one sputter source may be active during a“pass” made by the substrate.

[0060] Advantageously, first and second multi-anode sputter sources mayinclude targets of different metal and/or semi-metal materials to formsequential coatings of diverse metals, semi-metals, and their oxides ornitrides on the lens elements, the coatings having different indices ofrefractions. Layers are built up by repeatedly rotating the lenselements on the drum past the sputter sources. For example, the systemmay be used to apply a multi-layer oxide coating to columns of lenselements whose radially outwardly facing optical surfaces have beentreated with a hard coat. A five-layer coating comprising alternatinglayers of silicon oxide and zirconium oxide, the silicon oxide layersbeing outermost and innermost, is one such example.

[0061] The outer cylindrical face of the drum 22 is typically 2 to 9inches from the target surfaces of the sputter sources. The drum itselfmay be on the order of 40 inches in diameter and 40 inches high andcarry hundreds of articles 23 on its outer surface. Correspondingly, thesputter sources and plasma applicators (if present) may be on the orderof 40 inches in length. A preferred number of lens elements disposed onthe drum 22 is 200 to 450 articles 23.

[0062] The sputter source 30 illustrated in FIG. 2 will now be describedin more detail with reference to FIG. 3. The sputter source 30 comprisesa body 31, a target (cathode) 32, and a collection of anodes 33-1through 33-N where N is the total number of anodes. The anodes may beconfigured as electrically conductive bars and may be made of aluminum,aluminum alloys, copper, copper alloys, stainless steel, other alloys,or other conductive materials. Individual electrical connections aremade to the anodes and to the target (cathode) 32 using individualelectrical leads of the lead assembly 27. Alternatively, separateelectrical lead assemblies for the cathode and for the anodes may beused to provide the electrical connections. In the particular exampleshown in FIG. 3, there are eighteen anodes (N=18); however, it should beunderstood that the sputter source 30 may comprise a larger or smallernumber of anodes. The body 31 encloses an assembly of permanent magnets(not shown) that substantially confine the plasma to an oval shapedracetrack 34. Such magnet configurations are well known in the art.

[0063] The body 31 and the target 32 of the sputter source 30illustrated in FIG. 3 are substantially elongated and rectangular inshape. In addition the anodes may be disposed symmetrically in pairsalong opposing elongated sides of the sputter source body 31 with oneanode of an anode pair being disposed at one side of the target and theother anode of the pair being disposed at the opposing side of thetarget with both anodes positioned an equal distance from either end ofthe sputter source body 31. For example, in FIG. 3, opposing anodes 33-1and 33-10 comprise an anode pair, opposing anodes 33-2 and 33-11comprise an anode pair, and so forth. Insulating members (not shown) areprovided between the anodes and the body 31 to provide electricalisolation of the anodes from the body 31. The body 31 (which wouldnormally be the anode in the absence of the multi-anodes) will usuallybe attached to the chamber at ground potential. However this bodyrapidly becomes coated with insulating dielectric materials in reactivesputter coating so that the surface exposed to the plasma may float at apotential above ground potential and therefore lead to the well knownwandering anode problem which contributes to non-uniform sputterdeposition.

[0064] In a preferred embodiment according to FIGS. 2 and 3, the anodesof the sputter source 30 are configured to correspond to the placementand size of the articles 23 to be coated. Articles 23, such as plasticlens elements, are disposed uniformly on the drum 22 and may be arrangedin vertical columns and horizontal rows. The elongated sputter source 30is positioned vertically (parallel to the rotation axis of the drum 22)as shown in FIG. 2. The number of anode pairs may be equal to the numberof rows of articles 23 disposed on the drum 22. The anodes may beuniformly and symmetrically arranged in pairs at opposing sides of thetarget 32 wherein the separation between anodes of an anode pair is thesame for all anode pairs. Such a configuration is schematicallyillustrated in FIG. 4, which shows the projection of a column ofarticles 23 superimposed on a projection of the surface of the sputtertarget 32. In addition, pairs of anodes and rows of articles 23 arecentered in zones 4-1 through 4-9 separated vertically by horizontaldashed lines as illustrated in FIG. 4. It should be understood that thecolumn of articles 23 illustrated in FIG. 4 is displaced a distance awayfrom the sputter target 32.

[0065] In addition, according to this embodiment and as indicated inFIG. 4, the end regions of the sputter target 32 that encompass thecurved portions of the race track 34 are positioned in end zones 4-10and 4-11 that do not contain articles 23. It is advantageous to excludearticles 23 from the end zones 4-10 and 4-11 because the racetrack 34has a different geometrical configuration in the end zones compared tothe inner zones as illustrated in FIG. 4. Though not shown, anode pairsmay also be provided in end zones 4-10 and 4-11 to provide control ofthe plasma in these zones as well.

[0066] The configuration illustrated in FIG. 4 is characterized by ninepairs of anodes and nine rows of articles 23. It should be understood,however, that larger or smaller number of anode pairs and rows ofarticles 23 may be utilized. Configurations utilizing sputter sourcesranging from twenty to sixty inches in length having six to fifteenanode pairs are advantageous. The use of sputter sources approximatelyforty inches in length having from six or ten anode pairs is preferred.It is also preferred that anode pairs in the same zone be connectedtogether electrically and that they be supplied by means of a voltagelimited constant current source for each zone.

[0067] As shown in the configurations illustrated in FIG. 4, the anodesmay be configured with a length that is approximately equal to thevertical size of the articles 23. Such a configuration is advantageousfor controlling the thickness uniformity of the coating deposited on agiven article 23 as well as for controlling the coating thicknessuniformity between articles 23. Anodes substantially shorter than thezone length may be desirable under some process conditions toelectrically decouple them from one another.

[0068] The operation of the sputter source 30 will now be described inmore detail with reference to FIG. 4. A simple version of the controlscheme is shown in FIG. 4(a) wherein the variable resistors 41 areconnected to a single positive potential source 42. Anode 33-1 isconnected to anode 33-10 and then via the variable resistor 41 for zone4-1 to the source 42. Similarly anode 33-2 is connected to anode 33-10and then via the resistor 41 for zone 4-2 to the source 42 and so on.

[0069] The invention may be further understood by means of an examplewith reference to FIG. 4. Consider a 40-inch long by 5-inch wide silicontarget 32 mounted on the multi-anode sputter source 30. With eachvariable resistor 41 initially set to zero ohms, all anodes 33-1 through33-18 will be at ground potential. A voltage of −500 volts is applied tothe target (cathode) 32 resulting in a total current delivered to thetarget of approximately 18.0 amperes when the source is energized in anargon/oxygen atmosphere at a pressure of a few millitorr. The anodes arecontrolled in pairs via the variable resistors such that anodes 33-1 and33-10 form a pair, anodes 33-9 and 33-18 form a pair, and so forth.Given the target voltage and current noted above, each anode at groundpotential draws approximately 1.0 Amps of current; each pair of anodes,therefore, draws approximately 2.0 Amps.

[0070] For simplicity we will assume that, in the absence of the source42, with all variable resistors 41 set at zero, the multi anodes 33 areeffectively connected to ground potential so that the anode current persector is 2 Amps if they are all the same. The plasma impedance persector will therefore be 250 ohms. Suppose we now install the source 42and set it at +20 volts and set all the resistors 41 to 10 ohms. Assumethe anodes 33-1 through 33-18 are not covered by dielectric coatingswhereas the vacuum chamber walls in the vicinity of the sputter cathodes(and in the vicinity of the microwave applicator if present) are coatedwith insulating dielectrics and therefore will not act as effectiveground points. The cathode current (composed of electrons in the plasma)will therefore preferentially flow through the anodes 33-1 through 33-18to the positive potential VA. It is still desirable to have a currentflow of 2 Amps through each anode pair, the anode potential of each ofthe multi anodes will still be zero and the system will, to first order,operate as before. A major influence on the coating rate on articles onthe work holder opposite those zones is the plasma density in themwhich, to a measurable and significant extent, is controlled by theelectron current passing from cathode to anode in that zone.

[0071] Alternatively the positive supply 42 may be dispensed with andthe common terminals of all variable resistors 41 connected to a goodground potential. This scheme will only work if the anodes 33-1 through33-18 are effectively uncoated by dielectric whilst the chamber in thevicinity of the sputter magnetrons is substantially coated withelectrically insulating dielectrics and therefore does not provide agood ground potential. Under these circumstances the variable resistors41 can be used to adjust the anode currents up to the point where theanode potential becomes more negative than the effective ground plane ofthe nearby dielectrically coated chamber walls.

[0072] To provide more certainty than either of the previously discussedschemes for controlling the anode currents for each zone, it isdesirable to provide separate constant current power supplies for eachanode pair. These supplies may be set to a given voltage limit and aconstant current appropriate to each zone in order to provide thedesired uniformity profile Such an arrangement is shown in FIG. 4(b)which also illustrates a number of other preferred details of operation.In that Figure the anodes 33 are illustrated as wire brushes which haveseveral advantages as previously noted. The constant current powersupplies are indicated as 11 through 13 and these may be controlled byeither digital or analog means but in either case it is preferred thattheir outputs be adjustable under computer control. It may occur thatthe potentials developed on the anodes in an effort to control currentmay rise to levels sufficiently different on adjacent anodes that asubstantial current would flow between them. This is because they are tosome extent bathed in a plasma which aids such electrical conductionirrespective of the fact that they are, when not bathed in a plasma atleast, electrically insulated from the metal mounting bar on which theyare mounted via ceramic insulators or the like. To obviate thispossibility, it is desirable to install shields such as thoseillustrated as S12, S23 and S34 and so on between anode 33-1 and 33-2and between 33-2 and 33-3 and so on. As these and the mounting bar willordinarily become coated with insulating materials they will act as botha physical and an electrical barrier to the passage of current betweenadjacent anodes. The shields S12, S23 and S34 may be made ofelectrically insulated dielectric material.

[0073] In the embodiment illustrated in FIG. 3, adjacent anodes of themulti-anode sputter source 30 are separated by gaps 35. However, it maybe advantageous to minimize such gaps in order to facilitate spatialuniformity of the plasma. Accordingly, another embodiment of the presentinvention minimizes the gaps between adjacent anodes as illustrated inside view in FIG. 5(a).

[0074] In another embodiment, adjacent ends of anodes in a line may beseparated by a gap (for example a gap of 1 to 3 inches) or every otheranode in the line removed to reduce undesired coupling between theanodes through the plasma.

[0075]FIG. 5(a) schematically illustrates a multi-anode sputter source50 similar to that illustrated in FIGS. 3 and 4 but with a differentanode configuration to minimize gaps between adjacent anodes. Anodes53-1 through 53-N are uniformly and symmetrically disposed in pairs onopposing sides of a sputter target 52 in zones 5-1 through 5-10separated by horizontal dashed lines. The individual anodes are attachedto insulating mounting blocks 51 such that one end of each anode isdisposed closer to the sputter target 52 than the other end of thatanode. Further, except for mounting blocks 51 disposed near the ends ofthe sputter target 52, each mounting block 51 supports the ends of twoanodes separated by a gap 55 in the horizontal direction. The anodesdisposed at a given side of the sputter target 52 are thus positioned ina sawtooth-shaped arrangement as illustrated in FIG. 5(a). An identicalanode configuration is disposed at the opposing side of the sputtertarget 52.

[0076] Unlike the embodiment illustrated in FIGS. 3 and 4 whichpossesses a gap in the vertical direction between the anodes, theembodiment illustrated in FIG. 5(a) possesses a gap in the horizontaldirection with a minimal gap or no gap in the vertical direction. Thusin the vertical direction along the length of the sputter target 52, ananode surface is provided at substantially all vertical positions. Suchan anode configuration may be desirable for facilitating spatialuniformity of the sputter source plasma.

[0077] An alternative anode configuration that possesses a minimal gapor no gap in the vertical direction is illustrated in FIG. 5(b). In thisconfiguration, the anodes are disposed in a regular, sawtooth-shapedarrangement similar to that shown in FIG. 5(a). However, in theconfiguration shown in FIG. 5(b), anodes at opposing sides of thesputter target 52 are disposed in a mirror-image configuration.

[0078] A magnified illustration of one anode and two mounting blocks 51is shown in FIG. 5(c). Each mounting block has an array of mountingmeans 56 for mounting an anode to the block via fastening means (notshown) at the bottom surface of the anode. For example the mountingmeans 56 may be holes extending through the mounting block 51, and thefastening means (not shown) may be bolts extending from the bottomsurface of the anode. However, the mounting means 56 and the attachingmeans (not shown) are not to be limited to these examples.

[0079] In a preferred embodiment, an anode configuration such as thatshown in either FIG. 5(a) or FIG. 5(b) is provided with anodespossessing recessed slots 58 as illustrated in pictorial view in FIG.5(d) to maintain anode surfaces that remain substantially free ofcoating deposits. In FIG. 5(d), an anode is illustrated with a recessedslot 58 disposed at an angle with the opening of the slot pointing awayfrom the sputter target 52. Such recessed slots provide interior anodesurfaces that receive less coating deposits during sputter depositiondue to shadowing provided by the outer surfaces of the anode. This isespecially beneficial in the reactive sputtering of dielectric materials(oxides and nitrides, for example) to ensure good electrical conductionbetween the anodes and the plasma. Also shown in FIG. 5(d) are bolts 59as a particular example of fastening means extending from the bottomsurface of the anode. The bolts not only provide a means of fasteningthe anode to the mounting block (not shown), but also provide a means ofmaking electrical contact to the anode.

[0080] In another embodiment of the present invention, the multi-anodesputter source is configured with wire-brush anodes as illustrated inside view in FIGS. 6(a)-6(c). In FIG. 6(a) a sawtooth configuration ofwire-brush anodes 63-1 through 63-9 for placement along one elongatedside of a sputter source (not shown) is illustrated. It should beunderstood that an identical configuration or a mirror imageconfiguration of anodes (not shown) is disposed at the opposing side ofthe sputter source (not shown) in a manner such as that illustrated inFIG. 5(a) or FIG. 5(b).

[0081] A magnified side view of anode 63-1 is shown in FIG. 6(b). FIG.6(c) shows a cross-sectional view of anode 63-1, taken along plane A-Awherein a collection of individual metal wires 68 extends radially froma central electrically conducting support member 69. The central support69 and the metal wires 68 may be formed from a variety of materialsincluding, but not limited to, copper, brass, stainless steel, tungsten,and other electrical conductors. The density of wires 68 promoteseffective shadowing of individual wires 68, thus allowing the surfacesof numerous wires 68 to remain substantially free of coating deposits.This is especially beneficial in the reactive sputtering of dielectricmaterials (oxides and nitrides, for example) to ensure good electricalconduction between the anodes and the plasma. The copper containingbrush wires have the advantage that they tend to form conductive oxides.Sharp points on the ends of the wire lead to high electric fieldstrengths which lead to breakdown of any oxides deposited on them.

[0082] The wire-brush anodes 63-1 through 63-9 are shown as beingdisposed below the mounting blocks 61 in FIG. 6(a). However, it shouldbe understood that the wire-brush anodes may be attached to the tops ofthe mounting blocks 61 in a manner similar to that shown in FIGS. 5(a)and 5(b) that minimizes or eliminates vertical gaps between adjacentanodes. Alternatively, the wire-brush anodes may by configured in amanner similar to that shown in FIGS. 3 and 4, wherein vertical gapsexist between adjacent anodes.

[0083] The embodiments above have been described with reference to anelongated planar magnetron sputter source. However, it should beunderstood that the invention disclosed herein may be practiced inconjunction with a rotating cylindrical magnetron sputter source aswell. In this case, the multiple-anode configurations illustrated inFIGS. 2-6 are applied to a rotating cylindrical magnetron sputtersource.

[0084] The electrical control of the anodes discussed previously withreference to FIG. 4 utilized variable resistors electrically connectedbetween the anode and an electrical ground. However, control of theanodes may also be achieved with a multi-channel high-current powersupply such as the power supply 70 illustrated in FIG. 7(a).

[0085] The multi-channel high-current power supply 70 illustrated inFIG. 7(a) comprises a housing 711, a power supply cord 712 that deliverspower to the power supply 70, a main power switch 720 that controls thepower to the power supply, and ten channels that each control thevoltage and current delivered to a pair of anodes of the sputter source30. If desired, a channel of the power supply may be used to control asingle anode rather than a pair of anodes. Preferably, the power supply70 is rack mountable in a conventional electrical mounting rack.

[0086] Each channel of the power supply 70 comprises a voltage readout713, a current readout 714, a voltage control member 715, a currentcontrol member 716, and a channel power switch 717 to control power toan individual channel. Preferably the readouts 713 and 714 are digitalLED or LCD readouts. The control members 715 and 716 may be analog ordigital potentiometers.

[0087] Each channel of the power supply 70 also comprises amanual/remote switch 718 that allows an operator select between manualcontrol of the voltage and current using control members 715 and 716 orcomputer control of the voltage and current using an optionalcomputerized controller 750 shown in FIG. 7(b). The controller 750 maybe connected to the power supply 70 via interfaces at the rear of thecontroller 750 and power supply (not shown) using a detachableconnecting line 708.

[0088] The controller 750 illustrated in FIG. 7(b) comprises a CPU 751,a display 752, and a keyboard 753 connected to the CPU via a connectingline 754. The CPU 751 further comprises interfaces (not shown) at therear of the CPU for sending and receiving signals to and from themulti-channel power supply 70 and other equipment (not shown) of thedrum vacuum coating system 20. For example, the controller 750 maycontrol mass flow controllers (not shown) and receive signals frompressure measurement and voltage measurement equipment (not shown) forcontrolling the pressure, flow and ratios of sputtering gases such asargon, oxygen, nitrogen, and others.

[0089] The controller 750 may also receive signals from coatingthickness monitors such optical thickness monitors disposed in eachcoating zone shown in FIGS. 4 and 5 to provide real-time feedbackcontrol of the anode voltages. Such real-time feedback obtained fromoptical coating thickness monitors provides an advantageous method formaintaining coating thickness uniformity among the various coating zonesillustrated in FIGS. 4 and 5. The controller 750 may also be used tomonitor and control the cathode power supply (not shown). One purpose ofsuch control would be to adjust the total current from the cathode powersupply to match the total current applied to the anodes by means of theconstant current power supplies. Detachable signal lines 755 may be usedto pass electrical signals between the controller 750 and suchequipment.

[0090] As noted above a real-time feedback method utilizing signals fromoptical coating thickness monitors may be used to provide real-timecontrol of the anode currents via the controller 750 and themulti-channel high-current power supply 70 shown in FIGS. 7(a) and 7(b).Alternatively, post-deposition coating-thickness measurements may becarried out on articles coated during a given batch run to provideinformation that may be used to adjust the currents to anode pairs insubsequent runs. This latter approach provides a method for achievingcoating-thickness uniformity that is simple to implement and that doesnot require a computerized controller 750.

[0091] There are a number of subtleties to be considered in theimplementation of the multi anode scheme of control. Firstly it is usualthat the sputter power supply potential is switched to about 100 voltspositive for a brief period on a cyclic basis e.g. for about 20microseconds every 200 microseconds. The purpose of this is to dischargethe islands of metal oxide on the target which would otherwise build upcharge to the point where they would lead to an electrical breakdown ofthe oxide film and consequently cause a localized arc which has variousdeleterious effects. In a conventional system there is a difficulty withthis technique in that, as soon as the sputter power supply begins toreverse its polarity, the sputter plasma dies and there are fewelectrons left to neutralize the positive charge on the islands ofoxide. Furthermore, the few electrons which are left to do this duty arebottled up in the magnetic field of the sputter magnetron and are not atliberty to neutralize charge on the islands of oxide outside themagnetic bottle where they are most needed.

[0092] In a known conventional system (the MicroDyne™ System) theexistence of the microwave supported plasma nearby is supposed toovercome these difficulties in two ways. During the polarity reversal ofthe sputter power supply the microwave supported plasma is stilloperational and is able to supply the electrons needed to neutralize thecharged metal oxide islands. Furthermore, the electrons from themicrowave plasma are outside the magnetic bottle of the sputtermagnetron and are therefore able to reach said islands withoutdifficulty.

[0093] However, during the polarity reversal of the sputter powersupply, the constant current generators attached to the anodes aretrying to gather their allotted requirement of electron current which istypically on the order of two or a few amperes per anode pair. The dyingsputter plasma will not be able to supply this electron current duringsaid polarity reversal and the constant current power supplies willattempt to draw it from the surroundings, that is from the microwaveplasma if present. In any case the positive potential on these constantcurrent power supplies is likely to rise until they reach their voltagelimit at which point they will draw whatever electron current isavailable to them at that voltage limit and which may be significantlybelow the constant current set point. This is of no consequence to theoverall operation of the system with one important proviso: that theconstant current power supplies stay in or instantly return to theirconstant current mode when the sputter power supply ceases its briefcyclic polarity reversal.

[0094] The response of the system to an arc also bears consideration.When an arc occurs as described previously or due to other causes,modern sputter power supplies respond very quickly by lowering thecathode voltage from a few hundred volts negative potential to near zerovolts thus quenching the arc. The sputter power supply voltage may bekept near zero for some milliseconds to ensure the arc does not reoccurwhen the cathode voltage is returned to normal. During thisarc-quenching period the multi anode constant current power supplies areagain going to scour the surrounding volume for electrons and behave inthe same manner as previously described when the sputter plasma diesduring brief cyclic polarity reversals of the sputter power supply.However, in this case the impact on the microwave plasma will be oflonger duration and the drain of electrons from it may be evidenced by alonger period in which the microwave power source is mismatched to theplasma. The microwave power reflected from the plasma may havedeleterious effects on said microwave power source and these need to bemonitored and guarded against if necessary. At the cost of additionalcomplication it may be deemed necessary or desirable to shut down theconstant current power supplies to the multi anodes during periods ofsputter power supply polarity reversal or arc quenching.

[0095] Process Variable Monitoring and Control

[0096] In another preferred embodiment, a controller monitors processvariables and controls process parameters to improve batch-to-batchuniformity of coating thickness and coating composition.

[0097] Reactive sputtering systems have a large number of processvariables including the following: (1) oxygen partial pressure (2) argonpartial pressure (3) total system pressure (4) water vapor partialpressure (5) pump down time to base pressure (6) cathode voltage (7)kilowatt hours of use on each target since new (8) kilowatt hours oneach target since last target cleaning (9) number of minutes of dooropen between runs (10) calibration drifts and inaccuracies of vacuumgauges (11) contamination of gauges especially of the Optical GasController (12) test usage of targets for deposition of thick singlelayers (13) time since last shield clean (14) lens substrate type (15)lens hardcoat type (16) substrate pretreatment (17) lens form

[0098] Many of these process variables are directly or indirectlycontrollable. The interrelationships and dependencies of the variablesare complicated. Applicants have determined that the cathode voltage andtotal system pressure are sensitive indicators of the operating pointand thus of deposition rate. Applicants have also determined that it ispossible to take an expert system operator's knowledge of DC reactivesputter stabilization and effectively use it in a Fuzzy Logic ControlSystem for reactive sputter deposition.

[0099] Work with such a system indicates fuzzy logic control can improvebatch to batch stability by a factor of almost 5 using just two inputsand adjusting just two outputs. The two inputs used were Cathode Voltageand Total Pressure as measured on an MKS Baratron. The latter happens tobe one of the very few instruments used in a vacuum measurement whichhas very acceptable long term drift performance.

[0100] The fuzzy logic can effectively encode the knowledge of an expertoperator in systems which preferably have just a few important inputvariables and likewise just a few output controls. As the above listindicates, there are actually very many input variables to thedeposition process. However, as discussed below, a few key measuredparameters and controllable output variables can be identified.

[0101]FIG. 8 illustrates a fuzzy logic system of a preferred embodimentof the present invention. The fuzzy-logic controller is preferably usedto control the system. The anode currents are controlled utilizing thepower supply 70 with or without the controller 710 as described above.

[0102] As shown in FIG. 8, input signals corresponding to the magnitudeof the target (cathode) voltage and the total sputtering gas pressureare monitored by the fuzzy logic controller 800. Depending upon themagnitudes of the total gas pressure (X) and cathode voltage (Y), thecathode voltage and total pressure signals are categorized by thefuzzy-logic algorithm as high, medium, or low values.

[0103] The fuzzy-logic algorithm then applies predetermined rules basedon these categorizations to provide output signals to mass flowcontrollers to adjust the flow rates of sputtering gases A and B. Forexample, if the cathode-voltage signal is monitored (or set) as a “high”value, and the total pressure signal is monitored (or set) as a “medium”value, output signals corresponding to particular values of flow ratesare directed to the mass flow controller that controls the flow ofprocess gases A and B. The desired flow rates are determined by thefuzzy-logic controller according to rule-based algorithm. Input signalscorresponding to different categorizations of cathode voltage and totalpressure may yield different output signals resulting in different flowrates for the process gases (reactive and non-reactive) A and B. In thismanner, batch-to-batch uniformity of coating composition and coatingthickness is maintained. The fuzzy-logic rule-based algorithm may alsobe employed in the computer controller 710 rather than in a separatefuzzy logic controller 800.

[0104] It may be necessary to have some form of averaging processapplied to the inputs (cathode voltage and total pressure). Theaveraging period is tied to the natural time constants of themeasurement equipment, gas supply systems and the sputter processitself. An adaptive control system may be needed which in effectoperates like a servo system based on first and second derivatives ofthe error signal where the error signal is, for instance, the differencebetween the instantaneous value of an input parameter and its averagevalue as formed by the averaging process. The effect of this is to allowthe fuzzy logic system to quickly reach a point near the desiredoperating point and then settle closer to it on the basis of longer termaverages.

[0105] Because the process environment changes rapidly, the systememploys deterministic real-time control in order to guarantee processstability. LabVIEW RT (a product of National Instruments Co.) may beused as the software platform to run the fuzzy logic control routine.The software is run on a PXI-7030/6030E real-time data acquisition card.Besides the two analog I/O signals required for fuzzy control, the 6030Ealso required additional analog signals for process monitoring andadditional digital signals from an existing Programmable LogicController (PLC) which controlled sequencing of the batch. LabVIEW RTrunning on the Windows NT host PC was used for the user interface, datapresentation, saving data to file, additional SCADA functions via GPIBand Ethernet, and editing the fuzzy control strategy. A TransmissionControl Protocol (TCP) communication link is used to send fuzzy controlstrategies and commands to, and receive process data from, the LabVIEWprogram running on the real-time card. By separating the data andprocess control layers from the user interface and presentation layers,the process control algorithm can run reliably with deterministictiming. It is not affected by the CPU requirements of Windows NT orother programs running in Windows. LabVIEW RT made this possible.

[0106] LabVIEW RT allows the fuzzy logic control algorithms to be run ona real-time data acquisition card with an embedded processor. Exemplarysystem requirements are:

[0107] Real-Time Deterministic Control

[0108] Fuzzy Logic Controller

[0109] Analog Signal Interface for multiple Inputs and Outputs

[0110] Digital Signal Interface for Acquiring from a Programmable LogicController (PLC)

[0111] GPIB interface for Instrument Communication

[0112] Ethernet Interface for Communication to a Vacuum Control System

[0113] The National Instruments PXI platform may be used as the PCarchitecture for the system.

[0114] The Fuzzy Logic Toolkit for LabVIEW may be used as a basis for acustomized fuzzy logic editor. This editor allows the operator to easilytoggle between the membership functions of the inputs and outputs, aswell as edit the rulebases for both outputs. The amount of time requiredfor the operator to precisely tune to the control algorithm is reduced.As the system or product requirements change, the algorithm can bereadjusted to account for these changes.

[0115] Also, using the 3D graphing capabilities of LabVIEW 5.1, controlsurface plots can be created from the fuzzy logic controllers for theoperator to view. These plots can be rotated in 3 dimensions for carefulinspection (see FIGS. 12(a) and 12(b). The operator can zoom in onregions of interest when tuning the system.

[0116] Even though the inputs of the system are defined with impreciseterms like High, Low, and OK, the fuzzy logic system is actuallycompletely deterministic. For any set of input values there is a uniqueset of outputs. The fuzzy controller allows intuitive knowledge about aprocess to be realized in a controller.

[0117] The described fuzzy logic system uses only two out of the manypossible input parameters and uses only two outputs of a number ofpossible control outputs. The particular functions and rule strengthsetc. will be a function of the vacuum system; the materials beingdeposited, etc. An implementation and example of use of the techniquesin a particular system will now be discussed.

[0118] Fuzzy Logic Process

[0119]FIG. 9 is a flow diagram illustrating a preferred fuzzy logictechnique of the present invention. In the indicated first step 810, theinputs are “Fuzzified”, that is, classified into their membership offuzzy sets with linguistic definitions such as “low”, “OK” and “high”.The classification of Cathode Voltage and Total Pressure in the low, OKand high categories is shown in FIG. 10(a) and 10(b), respectively. Morespecifically, FIG. 10(a) shows the cathode voltage membership functionfor reactive sputtering of Niobium to form Niobia. FIG. 10(b) shows thecorresponding membership function for total pressure.

[0120] Evaluation of Rules

[0121] As a second step 812, a Rule Table is employed (based on expert'sknowledge or experimentation) which tells the system “what to do” withcontrol settings for all possible category combinations of the inputmembership functions.

[0122] The Rule Table for this example is shown below in Table I. TABLEI Sputter Voltage Sputter Pressure Flow Adjustment Low High ArgonDECREASE Low Low Oxygen INCREASE High High Oxygen DECREASE High LowArgon INCREASE OK High Argon DECREASE OK Low Argon INCREASE High OKOxygen DECREASE Low OK Oxygen INCREASE

[0123] Note that all other possible combinations of inputs not listed inTable I result in a HOLD condition for both Oxygen and Argon.

[0124] Table I entries are linguistically defined in a “fuzzy” manner,i.e. as “decrease”, “Hold”, “Increase”. The rules can be determined fromexperience or based on an understanding of the physics of the system.

[0125] Defuzzification

[0126] In the third step, 814, the linguistic “what to do” instructionsare “Defuzzified”, i.e. converted to actual numbers which change thecontrol settings (in the example, those for only Oxygen and Argonpressures).

EXAMPLE

[0127] The following is an example of a fuzzy logic control processcalculation. In the example, we shall assume that the instantaneousoperating point has drifted to a Cathode Voltage=370 Volts (Line A ofFIG. 10(a)) and a Total Pressure of 8.82 mBar (line B of FIG. 10(b)).From the graphs of FIG. 10(a), one may obtain a Voltage Membership 0.75“LO” and 0.25 “OK”. From the Pressure Membership Functions of FIG. 10(b)one may obtain the pressure membership values of 0.30 “OK and 0.70 “HI.(Note that these membership functions happen to add up to 1.00 in eachcase but they do not in general need to). These membership functionvalues are shown in the top left hand box of FIG. 11 which will be usedto track the calculation of the output for oxygen flow (i.e. percentvalve opening of a piezoelectric valve).

[0128] Next, the membership of the output sets (DECRease, HOLD,INCRease) for oxygen is calculated. Two Rules are used to do this. Theappropriate First Rule applied to the Pressure and Voltage membershipfunctions has been found to be Rule Strength—MINimum.

[0129] That is, as illustrated in the box of FIG. 11 labeled “RuleStrength MIN”. The output membership is determined for “Pressure OK” and“Voltage LO”=MIN (0.30, 0.75)=0.30 and so on for the other eight valuesin this box.

[0130] The Second Rule which has been found to apply to the result ofthe first rule is MAXimum, as illustrated in the box labeled “RuleStrength=MAX”. The resultant value for the membership function of HOLDis the maximum of all HOLD values=MAX (0.70, 0.00, 0.25, 0.25,0.00)=0.70. Likewise the resultant value for the membership function ofDECRease=MAX (0.30, 0.00)=0.30 and for INCRease=MAX (0.00, 0.00)=0.00.The “fuzzy” membership values of DECRease, HOLD and INCRease are nextconverted to “crisp” values which can be sent to an oxygen flowcontroller as a percentage of fully open of a piezoelectric valve ormass flow controller. We have chosen to do this by first constructingthe membership defuzzification functions illustrated in the graph at thebottom of FIG. 11 and then applying a “Center of Gravity” calculation to“crisipfy” the output value as a percentage opening value. The “Centerof Gravity” calculation can be envisaged as a balancing about thefulcrum point of 70% of the (DECR) area and 30% of the (HOLD) area toyield an output of (say) 81% valve opening.

[0131] It should be understood that the foregoing examples are adaptedto a particular sputter deposition system and material and wouldprobably require some modification for use with other systems andmaterials.

[0132] The controller should operate in real time to keep the operatingpoint stable during the deposition of each layer. It is desirable thatthe measurement cycle time of the control system be less than 50 msec.

[0133] As noted above, once all the rules and rule strengths of a FuzzyLogic Controller are established, the relationship between the inputsand the outputs are completely deterministic and can in principle and inpractice be replaced by a lookup table which gives the appropriateoutput values (oxygen and argon settings in our case) for any givencombination of input parameters (cathode voltage and total pressure asin the case of the foregoing example).

[0134] Indeed FIG. 12 indicates the type of three dimensional controlsurface that one can generate for oxygen flow and argon control versusthe two above mentioned input parameters. The fuzzy logic algorithms canbe used to provide a somewhat intuitive framework for developing rulesand membership functions. It is relatively easy, with such fuzzycontrols, to make intuitively understandable changes to the “low”, “OK”,“high” input regimes and the “DECR”ease, “HOLD”, “INCR”ease regimes ofthe outputs. This would be much more difficult using just a lookuptable. However, it may be noted that, once the lookup table has ineffect been established in the development phase, it may well be easierto implement such a lookup table.

[0135] The instant invention has been described with respect toparticular preferred embodiments and examples. The invention to beprotected, however, is intended to be defined by the literal language ofthe claims and the equivalents thereof.

We claim:
 1. A method for controlling the application of thin coatingsapplied to a substrate in a vacuum sputtering system, comprising:measuring an electrical parameter and a pressure parameter of thesputtering system during a sputtering run and producing measurementsignals indicative of the parameters; producing control signalsresponsive to said measurement signals based on a rule set; and usingsaid control signals to adjust in real time at least one process gasflow rate while sputtering.
 2. The method of claim 1, wherein theelectrical parameter measured is a cathode voltage and the pressureparameter measured is total system pressure.
 3. The method of claim 2,wherein the sputtering performed is reactive sputtering and the processgas flow rates that are controlled are a reactive gas flow rate and anon-reactive gas flow rate.
 4. The method of claim 1, wherein thecontrol signals are determined by a fuzzy-logic computation employingthe electrical parameter and the pressure parameter as inputs.
 5. Themethod of claim 1, wherein the control signals are determined from acomputerized look-up table based on the electrical parameter and thepressure parameter as inputs.
 6. The method of claim 5, wherein thelook-up table employs the following rule base: Cathode Voltage TotalSystem Pressure Flow Adjustment Low High Decrease non-reactive gas LowLow Increase reactive gas High High Decrease reactive gas High LowIncrease non-reactive gas OK High Decrease non-reactive gas OK LowIncrease non-reactive gas High OK Decrease reactive gas Low OK Increasereactive gas


7. The method of claim 5, wherein the look-up table employs a decisionstructure for adjusting the at least one process gas flow rate based ona categorization of the electrical parameter and a categorization of thepressure parameter.
 8. The method of claim 6, wherein the non-reactivegas is argon and the reactive gas is oxygen.
 9. A method for controllingthe application of a coating to a substrate in a coating system,comprising: measuring a first system parameter and a second systemparameter of the coating system during a coating run and producingmeasurement signals indicative of the system parameters; producingcontrol signals responsive to said measurement signals based on afuzzy-logic rule set; and using said control signals to control in realtime at least one process variable of the coating system while applyinga coating.
 10. The method of claim 9, wherein applying the coatingcomprises sputtering, wherein the first system parameter measured is acathode voltage of a sputtering source, and wherein the second systemparameter measured is a gas pressure.
 11. The method of claim 10,wherein the at least one process variable comprises a flow rate of afirst gas and a flow rate of a second gas.
 12. The method of claim 9,wherein the control signals are determined by a fuzzy-logic computationbased upon the first system parameter and the second system parameter asinputs.
 13. The method of claim 9, wherein the control signals aredetermined from a computerized look-up table based on the first systemparameter and the second system parameter as inputs.
 14. The method ofclaim 9, wherein the at least one process variable comprises a gaspartial pressure.
 15. A control system for controlling the applicationof a coating to a substrate in a coating system, comprising: afuzzy-logic controller; and an interface coupled to the fuzzy-logiccontroller, wherein the interface is configured to receive first andsecond measurement signals corresponding to first and second measuredsystem parameters, respectively, of a coating system during a coatingrun, wherein the fuzzy-logic controller is configured to receive thefirst and second measurement signals from the interface and to producecontrol signals responsive to said first and second measurement signalsbased on a fuzzy-logic rule set, and wherein the interface is configuredto provide the control signals produced by the fuzzy-logic controller tothe coating system to control at least one process variable of thecoating system during application of a coating.
 16. The control systemof claim 15, wherein the fuzzy-logic controller is configured to producethe control signals using a cathode voltage of a sputtering source asthe first measured system parameter and using a total system pressure asthe second measured system parameter.
 17. The control system of claim16, wherein the at least one process variable comprises a flow rate of afirst gas and a flow rate of a second gas.
 18. The control system ofclaim 15, wherein the fuzzy-logic controller is configured to producethe control signals using a fuzzy-logic computation based upon the firstmeasurement signal corresponding to the first measured system parameterand the second measurement signal corresponding to the second measuredsystem parameter as inputs.
 19. The control system of claim 15, whereinthe fuzzy-logic controller is configured to produce the control signalsusing a computerized look-up table based on the first measurement signalcorresponding to the first measured system parameter and the secondmeasurement signal corresponding to the second measured system parameteras inputs.
 20. The control system of claim 15, wherein the at least oneprocess variable comprises a gas partial pressure.